I want to start by appologizing if this has already been covered. But I looked and couldn't find the answer to my perticular problem. I have a '98 Civic EX. The check engine light came on with a P0420 code. As soon as the light came on the car started running rough and stalling out. Sometimes it takes several tries to get it restarted. Now if I clear the code it runs fine except for some hesitation accelerating to highway speeds. But eventually the code kicks out again and then i'm back to running rough. This has been going on for six months now and every time I replace something different. And every time I replace something i'm told it should take care of my problem. So far i've replaced the catalitic converter, both O2 sensors, spark plugs, plug wires, dist cap, rotor, ignition control module, distributor, fuel pump, and fuel filter. Pretty much in that order. The car has about 140,xxx miles on it and until this had no problems. I know the P0420 usualy refers to the cat or maybe the O2 but I've never heard of one going bad in 6 months. If anyone has any ideas I can try thanks in advance.